On 15/02/2014 23:12, DerbyBorn wrote:
PeterC wrote in
:

On Sat, 15 Feb 2014 19:13:39 GMT, Lobster wrote:

I've got a 100mm inline extractor fan in the ensuite; there's a vent
in the ceiling and it ducts the air up into the roofspace (in
corrugated flexible ducting) and as this is a dormer-style house with
a very low roofline, it passes down under the tiles in 100mm rigid
flat ducting to a grille just below the guttering.

It's really very ineffective though, and while I'm scrabbling around
in the roof space sorting out my downlighter wiring I thought I might
try fixing this too... I was considering replacing the 100mm fan with
a 150mm model; however, realistically there's no easy way to upgrade
the length of fixed 100mm ducting (about 1-1.5m worth) which runs
under the roof tiles. I would replace the flexible stuff in the roof
space with 150mm ducting, probably rigid rather than the flexible
hose.

Question is, would that be worthwhile at all? Would the old 100mm
section, which I can't upgrade, just act as a bottleneck to eliminate
any benefit?

Thanks

Rigid would, in itself, help, as corrugations cause a lot of drag.

Corrugations also allow a build up of fluff.

What is meant by "mixed flow"?



"In a mixed flow fan the air flows in both axial and radial direction
relative to the shaft. Mixed flow fans develops higher pressures than
axial fans."

Read mo http://www.engineeringtoolbox.com/fan-types-d_142.html
--
Dawood